In a service routing process, service nodes, such as a firewall, a Transmission Control Protocol (TCP) acceleration node, and a network address translation (NAT) node, that have network functions such as security authentication, filtering, statistical monitoring, charging, and flow acceleration form a network topology architecture of the service nodes, and are deployed on a path through which a service flow passes, so that when the service flow passes through these service nodes, a corresponding network function can be executed for the service flow.
However, in a network topology architecture deployed for a service, a quantity of service nodes changes, for example, the quantity of deployed service nodes is increased or decreased according to a change in a degree to which a network is busy, or the quantity is decreased when a fault occurs in a service node, that is, the quantity of service nodes deployed in the network topology architecture dynamically changes. For a packet flow in a service flow, when packets in the packet flow successively pass through service nodes of a hop, a quantity of the service nodes changes, for example, one service node is added, a problem that the packet flow is diverted (that is, service nodes through which the first several packets in the packet flow pass are different from service nodes through which the last several packets pass) may be caused. In this case, packet missequencing easily occurs in the packets in the packet flow. In addition, for a service node having a packet status recording requirement, the status recording requirement of the service node cannot be met.